1. Field of the Invention
The present invention relates to a camera module for an endoscope, which is mounted in a distal end of a probing portion of the endoscope inserted into a lumen or cavity of a test body.
2. Description of the Related Art
An endoscope has a camera module mounted in a distal end of a probing portion thereof, which is inserted into a lumen or cavity of a test body to be inspected with the endoscope. The camera module is a unit into which a taking lens and a circuit board, including an image sensor and a drive circuit for driving the image sensor, are integrated. The taking lens may include a movable lens and a lens drive mechanism for the movable lens to change the image magnification. The camera module is connected to a monitor that is installed outside the test body, so that images acquired from inside the lumen by the camera module may be displayed on the monitor.
The camera module is desired to be as small as possible for reducing the load on a patient when the endoscope is inserted into the patient. One problem against minimization of the camera module is that the circuit board takes a certain width or diameter in the camera module when the circuit board is positioned perpendicular to the optical axis of the taking lens. To solve this problem, JPA 2000-121957 suggests a camera module, in which a circuit board is positioned substantially parallel to the optical axis of a taking lens, and a prism disposed behind the taking lens refracts light from the subject toward the image sensor on the circuit board.
In the camera module of the above prior art, a movable lens for changing the image magnification is moved by rotating a rotary shaft which is directly coupled to a drive shaft of a motor. In this prior art, the motor for moving the movable lens is held in a notch that is formed in a cylindrical surface of a first ring of an angle ring and deformed to hold the motor in the distal end of the endoscope probing portion.
While the image sensor may not widen the endoscope probing portion in the above prior art, there will be dead or useless space behind the prism because the rotary shaft is directly coupled to the drive shaft of the motor. The dead space is obstructive to the reduction of diameter of the probing portion. Moreover, the direct coupling of the motor drive shaft to the rotary shaft results in increasing the length of the camera module along the optical axis of the taking lens, i.e. in the longitudinal direction of the probing portion.